Satellite Hinobe, un sole a quattro poli?

Diversi siti Web cospirazionisti hanno fatto eco in questi giorni a un lancio dell'Asahi Shinbun, il quotidiano giapponese, che riportava a sua volta il comunicato stampa del team di scienziati che analizzano i dati del satellite Hinode (Sunrise, nome assegnato dopo che nel pre-lancio, risalente al 2006, il satellite si era chiamato Solar-B), una missione congiunta JAXA, NASA e ESA che esplora in dettaglio l'attività magnetica del sole. La notizia riguarda un evento che a una lettura superficiale suona abbasanza inquietante. Il sole si sta trasformando in un gigantesco quadrupolo magnetico.

Il livello di risoluzione raggiunto da Hinode ha consentito in questi anni di rafforzare la nostra conoscenza sul fenomeno della "dinamo solare", l'effetto allla base della produzione delle celebri macchie, nonché degli eventi a esse correlati, come le eiezioni di massa coronale. Alla base della dinamo solare c'è il campo magnetico dell'astro: secondo la teoria le linee che congiungono i due poli del sole subiscono all'altezza dell'equatore una progressiva distorsione causata dalla diversa velocità angolare del sole alla latitudine bassa. Le linee tendono a spezzarsi, a richiudersi in maniera indipendente e a formare quindi delle "zone di interdizione" al calore che a loro volta si traducono in macchie solari (poi anche le linee del campo locale associate alle macchie si ricongiungono con le linee del campo magnetico totale dando vita agli effetti eiettivi, ma questo è un altro discorso).

In un comunicato rilasciato il 19 aprile (questa la versione originale in giapponese, ve la fornisco perché la traduzione con Google è abbastanza chiara e c'è un sacco di materiale aggiuntivo, molto meno rispetto alla traduzione inglese pubblicata nella versione del sito Hinode in questa lingua). In questi 4 anni, dice il comunicato, Hinode ha osservato in dettaglio il fenomeno dell'inversione di polarità che caratterizza, tra i tanti, il famoso ciclo solare. Ogni 11 anni circa, in corrispondenza del massimo solare, il picco di intensità raggiunto dal flusso e dal numero di macchie, i poli magnetici del sole si invertono rapidamente, il polo nord prende il posto del sud e viceversa. In base alle previsioni, questa inversione avrebbe dovuto verificarsi intorno al 2013, data appunto prevista per il nuovo massimo. Ma come forse sapete se leggete questo blog regolarmente, stiamo attraversando un periodo di intensità solare molto bassa, con un minimo di macchie che è stato prolungatissimo. Per quasi un anno anzi, il sole non ne ha praticamente avute, di macchie.

Che qualcosa stia succedendo (gli esperti ipotizzano un effetto di Dalton, o addirittura Maunder, due osservatori che nel '600 e alla fine del '700 hanno descritto periodi estremamente lunghi di minimo solare) sembrano ora testimoniarlo le osservazioni di Hinode. Quali sono le conclusioni degli astrofisici giapponesi? In quest'ultimo anno di rilevamento del flusso magnetico in corrispondenza delle regioni polari del sole si è rafforzato un fenomeno che va avanti dal 2008: il polo nord geografico del sole sta cambiando rapidamente la polarità magnetica. Normale, direte voi, con l'approssimarsi del massimo.

E invece no: il cambiamento di polarità sta accelerando, passando dal meno al più (la polarità dovrebbe cambiare già quest'anno) mentre non sta accadendo la stessa cosa al polo sud geografico, dove il segno più magnetico è assolutamente stabile. Le immagini che potete vedere, allegate a una recente testi di astrofisica e distribuite dai responsabili della missione Hinobe a corredo dei loro comunicati, sono molto evidenti. Al colore arancione corrisponde una polarità negativa, all'azzurro una positiva. Nell'immagine che riguarda le latitudini nord (coppia di immagini in alto) le chiazze arancione si diradano, cedono il posto all'azzurro (il confronto è 2008-2011 e 2009-2012), mentre alle estreme latitudini meridionali le chiazze azzurre dominano senza flessioni. Insomma, tra poco tempo rischiamo di avere un sole con quattro poli magnetici, due, positivi entrambi, in corrispondenza dei poli geografici; più verosimilmente altri due, ma col segno meno, in regioni equatoriali opposte tra loro. Un quadrupolo magnetico al posto di un dipolo.
Seguendo tale ragionamento, ci si potrebbe chiedere quali potrebbero essere le conseguenze di tale anomalia sulla dinamo solare. La quadrupla polarità potrebbe influire sul "motore" delle macchie solari, riducendone, come per una sorta di messa a terra, l'output complessivo e trascinando il sistema terra-sole verso le condizioni climatiche pre-glaciali che duecento e trecentocinquanta anni fa furono il "segno" più evidente dei minimi profondi. Nonché verso un probabile letargo delle onde corte sulle frequenze più alte.

Intanto, anche la NASA conferma, con la sua ultima stima sull'andamento del ciclo 24, che il prossimo massimo solare si raggiungerà nella primavera del 2o13 e sarà il meno intenso degli ultimi 100 anni, con un numero normalizzato di macchie pari a 60,2, contro i 118,4 del settembre 2000, in corrispondenza con il massimo del ciclo 23.

Macchie solari osservate prima che diventino macchie

Da oggi la meteorologia del sole dispone di uno strumento in più per anticipare le macchie e le tempeste magnetiche che si verificano sul nostro astro. In uno spettacolare studio appena pubblicato su Science, i ricercatori di Stanford hanno applicato i principi dell'analisi acustica predittiva utilizzati sul nostro pianeta dai sismologi, per anticipare l'emergere delle macchie solari sulla superficie del sole. Le macchie sono gigantesche aree di intensa attività magnetica che si formano nelle profondità dell'astro ed emergono letteralmente, come sottomarini, per effetto della spinta di galleggiamento magnetico. Analizzando i dati della sonda SOHO e dell'osservatorio solare SDO, i dottorandi di Stanford sono riusciti ad "ascoltare graficamente" le onde acustiche generate nel sole dai mostruosi fenomeni di convezione e a individuare così, in profondità e con molto anticipo rispetto all'effettivo emergere in superficie, il magnetismo delle macchie.

Una volta emerse, alle macchie solari si associano fenomeni come brillamenti ed espulsioni di massa coronale, che possono determinare eventi dirompenti a terra: tempeste geomagnetiche, interferenze alle telecomunicazioni, blackout sulle reti di distribuzione dell'energia elettrica.

Sunspot Breakthrough

August 25, 2011: Imagine forecasting a hurricane in Miami weeks before the storm was even a swirl of clouds off the coast of Africa—or predicting a tornado in Kansas from the flutter of a butterfly's wing1 in Texas. These are the kind of forecasts meteorologists can only dream about.

Could the dream come true? A new study by Stanford researchers suggests that such forecasts may one day be possible—not on Earth, but on the sun.

"We have learned to detect sunspots before they are visible to the human eye," says Stathis Ilonidis, a PhD student at Stanford University. "This could lead to significant advances in space weather forecasting."

Sunspots are the "butterfly's wings" of solar storms. Visible to the human eye as dark blemishes on the solar disk, sunspots are the starting points of explosive flares and coronal mass ejections (CMEs) that sometimes hit our planet 93 million miles away. Consequences range from Northern Lights to radio blackouts to power outages.

Astronomers have been studying sunspots for more than 400 years, and they have pieced together their basic characteristics: Sunspots are planet-sized islands of magnetism that float in solar plasma. Although the details are still debated, researchers generally agree that sunspots are born deep inside the sun via the action of the sun’s inner magnetic dynamo. From there they bob to the top, carried upward by magnetic buoyancy; a sunspot emerging at the stellar surface is a bit like a submarine emerging from the ocean depths.

In the August 19th issue of Science, Ilonidis and co-workers Junwei Zhao and Alexander Kosovichev announced that they can see some sunspots while they are still submerged.

Their analysis technique is called "time-distance helioseismology2," and it is similar to an approach widely used in earthquake studies. Just as seismic waves traveling through the body of Earth reveal what is inside the planet, acoustic waves traveling through the body of the sun can reveal what is inside the star. Fortunately for helioseismologists, the sun has acoustic waves in abundance. The body of the sun is literally roaring with turbulent boiling motions. This sets the stage for early detection of sunspots.

"We can't actually hear these sounds across the gulf of space," explains Ilonidis, "but we can see the vibrations they make on the sun's surface." Instruments onboard two spacecraft, the venerable Solar and Heliospheric Observatory (SOHO) and the newer Solar Dynamics Observatory (SDO) constantly monitor the sun for acoustic activity.

Submerged sunspots have a detectable effect on the sun's inner acoustics—namely, sound waves travel faster through a sunspot than through the surrounding plasma. A big sunspot can leapfrog an acoustic wave by 12 to 16 seconds. "By measuring these time differences, we can find the hidden sunspot."

Ilonidis says the technique seems to be most sensitive to sunspots located about 60,000 km beneath the sun’s surface. The team isn't sure why that is "the magic distance," but it's a good distance because it gives them as much as two days advance notice that a spot is about to reach the surface.

"This is the first time anyone has been able to point to a blank patch of sun and say 'a sunspot is about to appear right there,'" says Ilonidis's thesis advisor Prof. Phil Scherrer of the Stanford Physics Department. "It's a big advance."

"There are limits to the technique," cautions Ilonidis. "We can say that a big sunspot is coming, but we cannot yet predict if a particular sunspot will produce an Earth-directed flare."

So far they have detected five emerging sunspots—four with SOHO and one with SDO. Of those five, two went on to produce X-class flares, the most powerful kind of solar explosion. This encourages the team to believe their technique can make a positive contribution to space weather forecasting. Because helioseismology is computationally intensive, regular monitoring of the whole sun is not yet possible—"we don’t have enough CPU cycles," says Ilonidis —but he believes it is just a matter of time before refinements in their algorithm allow routine detection of hidden sunspots.

The original research reported in this story may be found in Science magazine: "Detection of Emerging Sunspot Regions in the Solar Interior" by Ilonidis, Zhao and Kosovichev, 333 (6045): 993-996.

Ciclo 24, un massimo davvero al minimo

Un ciclo solare, il numero 24 attualmente in corso, che dovrebbe raggiungere un massimo poco prominente, tra circa due anni e mezzo. Queste sono le prime previsioni formulate dagli esperti di fisica solare del Marshall Space Flight Center della NASA, disponibili qui. Allo stato le previsioni dicono che il massimo raggiungerà un numero di macchie normalizzato pari a 64 (davvero poco) verso il luglio 2013. Proseguendo il suo cammino, il ciclo che è da poco iniziato fornirà ulteriori indizi. Ecco un riassunto delle tre tecniche utilizzate dagli scienziati per questo tipo di proiezioni.

(...)

Among the most reliable techniques are those that use the measurements of changes in the Earth's magnetic field at, and before, sunspot minimum. These changes in the Earth's magnetic field are known to be caused by solar storms but the precise connections between them and future solar activity levels is still uncertain.

Of these "geomagnetic precursor" techniques three stand out. The earliest is from Ohl and Ohl [Solar-Terrestrial Predictions Proceedings, Vol. II. 258 (1979)] They found that the value of the geomagnetic aa index at its minimum was related to the sunspot number during the ensuing maximum. The primary disadvantage of this technique is that the minimum in the geomagnetic aa index often occurs slightly after sunspot minimum so the prediction isn't available until the sunspot cycle has started.

An alternative method is due to a process suggested by Joan Feynman. She separates the geomagnetic aa index into two components: one in phase with and proportional to the sunspot number, the other component is then the remaining signal. This remaining signal has, in the past, given good estimates of the sunspot numbers several years in advance. The maximum in this signal occurs near sunspot minimum and is proportional to the sunspot number during the following maximum. This method does allow for a prediction of the next sunspot maximum at the time of sunspot minimum.

A third method is due to Richard Thompson [Solar Physics 148, 383 (1993)]. He found a relationship between the number of days during a sunspot cycle in which the geomagnetic field was "disturbed" and the amplitude of the next sunspot maximum. His method has the advantage of giving a prediction for the size of the next sunspot maximum well before sunspot minimum.

(...)

Nuove previsioni per un sole "senza macchia"

C'è un supplemento di indagine allo studio che i due ricercatori del National Solar Observatory Matthew Penn e William Livingston avevano pubblicato lo scorso anno a proposito del progressivo calo di intensità del campo magnetico associato alle macchie solari. Le macchie sul sole, sostengono i due scienziati, stanno attraversando una fase di calo quantitativo e qualitativo. Le conclusioni della nuova ricerca pubblicata in occasione dell'ultimo simposio IAU, segnalato su Science parlano di un futuro "immacolato" per il nostro sole. L'attuale ciclo 24 potrebbe avere un numero complessivo di macchie pari alla metà del valore registrato nel ciclo appena trascorso. Il ciclo 25, tra una decina d'anni, potrebbe essere "spotless". In pratica un nuovo minimo di Maunder che potrebbe verificarsi tra il 2015 e il 2020.

Queste osservazioni sono molto specifiche e non dicono quali potrebbero gli effetti complessivi su fenomeni come i brillamenti e eiezioni di massa coronale, che hanno un impatto diretto sulla ionosfera e sul campo magnetico della terra. Certo è che l'ultima parte del ciclo 23 è stata caratterizzata da un minimo prolungato e un lungo periodo a macchie zero.

Il sole riprende fiducia: macchie a gogo e rischi al GPS

In fin dei conti l'allarmismo che ha circondato il prolungarsi del minimo solare al termine del ciclo precedente si è rivelato infondato. Qualcuno temeva che il sole avesse esaurito la scorta di macchie ma non è così, l'astro in questi giorni è ripartito in tromba, con un imponente gruppo di macchie qui fotografato dal pisano Stefano Pello, gruppo classificato con il numero 1045.
Alle macchi si associa il fenomeno delle radioemissioni in banda decametrica, cioè nelle onde corte. Thomas Ashcraft su Heliotown.com ha pubblicato impressionanti registrazioni mp3 del ruggito delle macchie, utilizzando - rivela il sito Spaceweather - antenne utilizzate per le ricerche radioastronomiche in HF, come quelle dell'Osservatorio di Nançay.

RADIO-ACTIVE SUNSPOT: Behemoth sunspot 1045 is crackling with M-class solar flares--and that's not all. "There have been many loud shortwave radio bursts over the past two days," reports amateur radio astronomer Thomas Ashcraft of New Mexico. "Some of the bursts have completely saturated my receivers." Just listen to the sounds coming from the loudspeakers in his observatory.
The roaring sounds you just heard were mainly Type III radio bursts, caused by beams of electrons streaming through the sun's outer atmosphere. Sunspot 1045 appears poised to explosively accelerate more electrons in the days ahead as the flare-show continues. Ham radio operators, point your Yagis toward the sun!
Per essere sempre aggiornati su questi fenomeni e avere la possibilità di osservare l'attività magnetica del sole in diretta e in tre dimensioni, ora potete scaricare l'applicazione iPhone 3DSun, realizzata appositamente dalla NASA. Tutte le informazioni del caso sul sito 3DSun.org
o direttamente su iTunes Store (app gratuita)

L'attività solare tornata a crescere ha un risvolto molto inquietante nel possibile effetto sul sistema di navigazione satellitare GPS. Intervistando i ricercatori della University of Bath, la BBC scrive che le turbolenze magnetiche e particellari solari possono determinare pericolosi disservizi nei satelliti che regolano ormai una parte fondamentale dei nostri trasporti, dal traffico aereo civile a milioni di automobilisti. E' curioso come l'allarme venga lanciato solo dopo lo smantellamento deciso per sistemi di radionavigazione terrestre come il LORAN-C, di cui abbiamo dato notizia l'altro giorno. Affidarsi solo ai satelliti è una strategia intelligente? Se è vero che i fenomeni solari impattano anche sulle trasmissioni dei radiofari e di sistemi VLF come il LORAN, forse dovremmo conservare - per prudenza - anche qualche sistema di backup. Negli USA un gruppo di radioamatori si è offerto volontario per il mantenimento della rete appena chiuda dall'Amministrazione Obama.

Sat-nav devices face big errors as solar activity rises
By Jason Palmer Science and technology reporter, BBC News

Researchers say the Sun is awakening after a period of low activity, which does not bode well for a world ever more dependent on satellite navigation.

The Sun's irregular activity can wreak havoc with the weak sat-nav signals we use.
The last time the Sun reached a peak in activity, satellite navigation was barely a consumer product. But the Sun is on its way to another solar maximum, which could generate large and unpredictable sat-nav errors. It is not just car sat-nav devices that make use of the satellite signals; accurate and dependable sat-nav signals have, since the last solar maximum, quietly become a necessity for modern infrastructure.
Military operations worldwide depend on them, although they use far more sophisticated equipment. Sat-nav devices now form a key part of emergency vehicles' arsenals. They are used for high-precision surveying, docking ships and they may soon be used to automatically land commercial aircraft.
(continua)

E se le macchie solari sparissero?

Il sito Spaceweather ha appena pubblicato un approfondimento della notizia relativa a uno studio sulla variabilità magnetica delle macchie solari, le quali, secondo due astrofisici del National Solar Observatory di Tucson, stanno perdendo visibilmente intensità. Il sito è andato a chiedere direttamente il parere dei due studiosi, che ammettono che a fronte di una simile perdita di intensità non è del tutto da escludere l'ipotesi che le macchie solari, che sono appunto legate all'intensità dei campi magnetici, spariscano quasi completamente. Ci sono insomma condizioni solari compatibili con il celebre minimo di Maunder, che iniziò nel 1645 e si prolungò per oltre 70 anni. Altri esperti ritengono che il sole si è semplicemente addormentato un po', che entro un anno tutto ripartirà.
Un paio di giorni prima il sito aveva pubblicato un altro articolo che fa riflettere sulle possibile conseguenze di questo profondo minimo solare sul sistema geomagnetico. Il 2 settembre 1859 durante un massimo a bassa intensità come quello che si prevede nei prossimi 3 o 4 anni, fu registrata a terra una tempesta geomagnetica di proporzioni colossali, con l'aurora boreale visibile addirittura a Cuba. Il giorno prima l'astronomo dilettante Richard Carrington aveva avvistato e descritto un potentissimo brillamento sulla superficie del sole, in corrispondenza di un esteso gruppo di macchie. A terra, i fili dei telegrafi si caricarono al punto da provocare scintille, danneggiando gli apparecchi riceventi e addirittura infiammando le strisce di carta degli inchiostratori. La morale? Che anche un minimo solare o un ciclo a bassa intensità possono fare da sfondo a tempeste geomagnetiche di grandi proporzioni. Anche dal punto di vista propagative, la mia esperienza di cicli solari e correlazioni con la ricezione di segnali lontani mi induce a credere che non si debba temere un blackout delle onde corte o delle aperture in E sporadico in FM. In questo fine settimana sentivo cose molto interessanti, incluso il servizio per le forze armate americane ripetuto dalla base nel Pacifico alle isole Hawaii, e molti segnali interessanti nelle bande alte radioamatoriali. La stagione dell'E sporadico non è stata eccezionale, ma sembra ormai chiaro che il fenomeno non è fortemente correlato all'andamento del ciclo.

Are Sunspots Disappearing?
09.03.2009

September 3, 2009: The sun is in the pits of the deepest solar minimum in nearly a century. Weeks and sometimes whole months go by without even a single tiny sunspot. The quiet has dragged out for more than two years, prompting some observers to wonder, are sunspots disappearing?
"Personally, I'm betting that sunspots are coming back," says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson, Arizona. But, he allows, "there is some evidence that they won't."
Penn's colleague Bill Livingston of the NSO has been measuring the magnetic fields of sunspots for the past 17 years, and he has found a remarkable trend. Sunspot magnetism is on the decline: "Sunspot magnetic fields are dropping by about 50 gauss per year," says Penn. "If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015."
This disappearing act is possible because sunspots are made of magnetism. The "firmament" of a sunspot is not matter but rather a strong magnetic field that appears dark because it blocks the upflow of heat from the sun's interior. If Earth lost its magnetic field, the solid planet would remain intact, but if a sunspot loses its magnetism, it ceases to exist.
"According to our measurements, sunspots seem to form only if the magnetic field is stronger than about 1500 gauss," says Livingston. "If the current trend continues, we'll hit that threshold in the near future, and solar magnetic fields would become too weak to form sunspots."
"This work has caused a sensation in the field of solar physics," comments NASA sunspot expert David Hathaway, who is not directly involved in the research. "It's controversial stuff."
The controversy is not about the data. "We know Livingston and Penn are excellent observers," says Hathaway. "The trend that they have discovered appears to be real." The part colleagues have trouble believing is the extrapolation. Hathaway notes that most of their data were taken after the maximum of Solar Cycle 23 (2000-2002) when sunspot activity naturally began to decline. "The drop in magnetic fields could be a normal aspect of the solar cycle and not a sign that sunspots are permanently vanishing."
Penn himself wonders about these points. "Our technique is relatively new and the data stretches back in time only 17 years. We could be observing a temporary downturn that will reverse itself."
The technique they're using was pioneered by Livingston at the McMath-Pierce solar telescope near Tucson. He looks at a spectral line emitted by iron atoms in the sun's atmosphere. Sunspot magnetic fields cause the line to split in two—an effect called "Zeeman splitting" after Dutch physicist Pieter Zeeman who discovered the phenomenon in the 19th century. The size of the split reveals the intensity of the magnetism.
Astronomers have been measuring sunspot magnetic fields in this general way for nearly a century, but Livingston added a twist. While most researchers measure the splitting of spectral lines in the visible part of the sun's spectrum, Livingston decided to try an infra-red spectral line. Infrared lines are much more sensitive to the Zeeman effect and provide more accurate answers. Also, he dedicated himself to measuring a large number of sunspots—more than 900 between 1998 and 2005 alone. The combination of accuracy and numbers revealed the downturn.
If sunspots do go away, it wouldn't be the first time. In the 17th century, the sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists. The sunspot drought began in 1645 and lasted until 1715; during that time, some of the best astronomers in history (e.g., Cassini) monitored the sun and failed to count more than a few dozen sunspots per year, compared to the usual thousands.
"Whether [the current downturn] is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen," Livingston and Penn caution in a recent issue of EOS. "Other indications of solar activity suggest that sunspots must return in earnest within the next year."
Whatever happens, notes Hathaway, "the sun is behaving in an interesting way and I believe we're about to learn something new."

GEOMAGNETIC MEGA-STORM: On Sept. 2nd, a billion-ton coronal mass ejection (CME) slammed into Earth's magnetic field. Campers in the Rocky Mountains woke up in the middle of the night, thinking that the glow they saw was sunrise. No, it was the Northern Lights. People in Cuba read their morning paper by the red illumination of aurora borealis. Earth was peppered by particles so energetic, they altered the chemistry of polar ice.
Hard to believe? It really happened--exactly 150 years ago. This map shows where auroras were sighted in the early hours of Sept. 2, 1859:
As the day unfolded, the gathering storm electrified telegraph lines, shocking technicians and setting their telegraph papers on fire. The "Victorian Internet" was knocked offline. Magnetometers around the world recorded strong disturbances in the planetary magnetic field for more than a week.
The cause of all this was an extraordinary solar flare witnessed the day before by British astronomer Richard Carrington. His sighting marked the discovery of solar flares and foreshadowed a new field of study: space weather. According to the National Academy of Sciences, if a similar flare occurred today, it would cause $1 to 2 trillion in damage to society's high-tech infrastructure and require four to ten years for complete recovery.
A repeat of the Carrington Event seems unlikely from our low vantage in a deep solar minimum--but don't let the quiet fool you. Strong flares can occur even during weak solar cycles. Indeed, the Carrington flare itself occured during a relatively weak cycle similar to the one expected to peak in 2012-2013. Could it happen again? Let's hope not.

Le macchie solari si stanno lentamente spegnendo?

Quarantaquattro. Gatti? No, giorni - a oggi - senza macchie solari. Il minimo magnetico del nostro astro comincia a preoccupare seriamente i ricercatori. A inizio luglio, la comparsa della macchia numero 1024 aveva fatto illudere un po' tutti segnando un pur timido inizio del ciclo 24. Passata la macchia, gabbato lo sole: da allora tutto è tornato quieto e il disco solare continua a essere immacolato, con i valori geomagnetici che in effetti si mantengono sempre molto bassi. Dal punto di vista propagativo le cose per i segnali radio deboli e lontani sembrano andare a senso alterno. Qui a L'Ago ieri e stamattina la presenza dell'Alaska nei 25 metri della banda broadcast è un buon indicatore, anche nelle bande amatoriali dei 20 metri, quindi su frequenze abbastanza alte che a rigor di logica sarebbero favorite dall'attività solare, ci sono segnali interessanti. In FM la stagione dell'E sporadico si sta chiudendo con gli ultimi fuochi delle aperture in Europa (qui in Italia con la banda così affollata, è difficile rendersene conto): non è stata una grande stagione ma si deve anche dire che l'E sporadico non sembra essere del tutto correlato all'attività solare, ci possono essere aperture molto intense anche senza macchie solari. In compenso oltreoceano segnalano già le aperture in onde medie, transatlantiche e transpacifiche. Ho provato ad ascoltare qualcosa nella mia postazione ligure, ma tra venerdì e sabato non c'era granché, mentre ieri le fortissime scariche elettriche atmosferiche mi hanno fatto desistere. Interessante la frequenza di 638 kHz (separata di un kHz dal canale europeo dei 639), dove dopo il tramonto si può ascoltare, con difficoltà, NBC Nigeria da Kaduna.
E il sole? Oggi su Space Weather c'è un articolo piuttosto allarmante di due studiosi del National Solar Observatory di Tucson, in Arizona, che hanno calcolato una netta diminuzione nell'intensità del campo magnetico associato alle macchie solari. Gli scienziati hanno lavorato misurando l'effetto Zeeman, che determina un diverso comportamento degli elettroni in presenza di campi magnetici costanti (elettroni con diverso numero quantito interagiscono in modo diverso e non passano più tra livelli energetici fissi ma "splittati") sugli atomi di ferro prossimi alle macchie solari. Dalle loro analisi emerge che la separazione Zeeman delle linee spettrali osservate è meno marcata e quindi il campo che genera le macchie è in proporzione più basso. E senza campo, le macchie possono - come si vede - scomparire del tutto.
Insomma, un minimo davvero minimo, che giustamente viene paragonato a quello della Borsa (arrivato in basso scende ancora più in basso) e comporta, oltre al crollo delle emissioni radio a 10,7 centimetri di lambda (mai così basse in 55 anni di misurazioni), anche un calo dell'irraggiamento.



Nel caso dei raggi UV estremi è addirittura del 6%, non abbastanza per invertire gli effetti del riscaldamento globale ma sufficiente per determinare, per esempio, un minor rigonfiamento degli strati alti dell'atmosfera (meno caldi) con una conseguente dimunuzione dell'attrito sui satelliti a orbita bassa, che diventano più longevi (con loro sono più longevi anche i detriti spaziali e questo è meno bello).

QUIET SUN: Today marks the 44th consecutive day without spots on the sun--one of the longest quiet spells of the current solar minimum. In early July, sunspot 1024 seemed to herald the long-awaited onset of Solar Cycle 24, but shortly after that apparition, sunspot production turned off again. Deep solar minimum continues...
ARE SUNSPOTS DISAPPEARING? Sunspots are made of magnetism. The "firmament" of a sunspot is not matter but rather a strong magnetic field that appears dark because it blocks the upflow of heat from the sun's fiery depths. Without magnetism, there would be no sunspots.

That's what makes the following graph a little troubling:


According to Bill Livingston and Matt Penn of the National Solar Observatory in Tucson, Arizona, sunspot magnetic fields are waning. The two respected solar astronomers have been measuring solar magnetism since 1992. Their technique is based on Zeeman splitting of infrared spectral lines emitted by iron atoms in the vicinity of sunspots. Extrapolating their data into the future suggests that sunspots could completely disappear within decades. That would be a bummer for Spaceweather.com.
Don't count out sunspots just yet, however. While the data of Livingston and Penn are widely thought to be correct, far-reaching extrapolations may be premature. This type of measurement is relatively new, and the data reaches back less than 17 years. "Whether this is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen," they caution in a recent EOS article.
One thing is certain. Solar Minimum is a lot more interesting than it sounds: more.

Minimo solare senza macchie, scoperta la causa?

Gli scienziati del National Solar Observatory di Tucson, Arizona, potrebbero aver individuato la ragione del prolungato minimo che caratterizza da parecchi mesi il ciclo di attività solare. Nella profondità dell'astro esiste una "corrente a getto" che si muove come le correnti oceaniche o analoghi fenomeni atmosferici. Come spiega Spaceweather.com sarebbe questa corrente a partecipare a "innescare" il ciclo delle macchie solari e dei fenomeni ad esse associate: quando la corrente raggiunge una determinata latitudine del globo solare, i 22 gradi, le macchie ripartono. Negli ultimi tre o quattro anni, dicono i ricercatori di Tucson che si sono serviti di avanzate tecniche di indagine "eliosismica", la corrente a getto interna si è mossa con inusistata lentezza. La scoperta sembra confermare anche che il lungo minimo è arrivato alla fine perché la corrente in quesione si sta di nuovo muovendo. Contrariamente alle previsioni di alcuni, le macchie torneranno a ricoprire il disco del sole.

Mystery of the Missing Sunspots, Solved?
06.17.2009


June 17, 2009: The sun is in the pits of a century-class solar minimum, and sunspots have been puzzlingly scarce for more than two years. Now, for the first time, solar physicists might understand why. At an American Astronomical Society press conference today in Boulder, Colorado, researchers announced that a jet stream deep inside the sun is migrating slower than usual through the star's interior, giving rise to the current lack of sunspots.
Rachel Howe and Frank Hill of the National Solar Observatory (NSO) in Tucson, Arizona, used a technique called helioseismology to detect and track the jet stream down to depths of 7,000 km below the surface of the sun. The sun generates new jet streams near its poles every 11 years, they explained to a room full of reporters and fellow scientists. The streams migrate slowly from the poles to the equator and when a jet stream reaches the critical latitude of 22 degrees, new-cycle sunspots begin to appear.
Howe and Hill found that the stream associated with the next solar cycle has moved sluggishly, taking three years to cover a 10 degree range in latitude compared to only two years for the previous solar cycle.
The jet stream is now, finally, reaching the critical latitude, heralding a return of solar activity in the months and years ahead. "It is exciting to see", says Hill, "that just as this sluggish stream reaches the usual active latitude of 22 degrees, a year late, we finally begin to see new groups of sunspots emerging."
The current solar minimum has been so long and deep, it prompted some scientists to speculate that the sun might enter a long period with no sunspot activity at all, akin to the Maunder Minimum of the 17th century. This new result dispells those concerns. The sun's internal magnetic dynamo is still operating, and the sunspot cycle is not "broken."
Because it flows beneath the surface of the sun, the jet stream is not directly visible. Hill and Howe tracked its hidden motions via helioseismology. Shifting masses inside the sun send pressure waves rippling through the stellar interior. So-called "p modes" (p for pressure) bounce around the interior and cause the sun to ring like an enormous bell. By studying the vibrations of the sun's surface, it is possible to figure out what is happening inside. Similar techniques are used by geologists to map the interior of our planet.
In this case, researchers combined data from GONG and SOHO. GONG, short for "Global Oscillation Network Group," is an NSO-led network of telescopes that measures solar vibrations from various locations around Earth. SOHO, the Solar and Heliospheric Observatory, makes similar measurements from space.
"This is an important discovery," says Dean Pesnell of NASA's Goddard Space Flight Center. "It shows how flows inside the sun are tied to the creation of sunspots and how jet streams can affect the timing of the solar cycle. We still don't understand exactly how jet streams trigger sunspot production," says Pesnell. "Nor do we fully understand how the jet streams themselves are generated."
To solve these mysteries, and others, NASA plans to launch the Solar Dynamics Observatory (SDO) later this year. SDO is equipped with sophisticated helioseismology sensors that will allow it to probe the solar interior better than ever before. "The Helioseismic and Magnetic Imager (HMI) on SDO will improve our understanding of these jet streams and other internal flows by providing full disk images at ever-increasing depths in the sun," says Pesnell.

Macchie solari, un minimo prolungato

Teoricamente doveva essere passato. E invece sembra proprio che il minimo di questo ciclo, il 24, non arrivi mai. Il 2008 è stato caratterizzato da un record di 266 giorni senza macchie (solo il 1913 era stato più avaro di formazioni sul disco solare). Ma nei primi 90 giorni del 2009 quelli senza macchie sono stati ben 78. Secondo gli scienziati della NASA stiamo vivendo un minimo prolungato dopo cinque cicli undecennale molto intensi. Quanto durerà? Non si sa, ma intanto le conseguenze sono una riduzione dell'attività aurorale e molto altro. Le osservazioni dimostrano per esempio che anche fenomeni come il vento solare, le emissioni radio o la stessa radianza dell'astro, hanno subito una contrazione in questi ultimi anni.

Deep Solar Minimum
04.01.2009

April 1, 2009: The sunspot cycle is behaving a little like the stock market. Just when you think it has hit bottom, it goes even lower.
2008 was a bear. There were no sunspots observed on 266 of the year's 366 days (73%). To find a year with more blank suns, you have to go all the way back to 1913, which had 311 spotless days: plot. Prompted by these numbers, some observers suggested that the solar cycle had hit bottom in 2008.
Maybe not. Sunspot counts for 2009 have dropped even lower. As of March 31st, there were no sunspots on 78 of the year's 90 days (87%).
It adds up to one inescapable conclusion: "We're experiencing a very deep solar minimum," says solar physicist Dean Pesnell of the Goddard Space Flight Center.
"This is the quietest sun we've seen in almost a century," agrees sunspot expert David Hathaway of the Marshall Space Flight Center.
Quiet suns come along every 11 years or so. It's a natural part of the sunspot cycle, discovered by German astronomer Heinrich Schwabe in the mid-1800s. Sunspots are planet-sized islands of magnetism on the surface of the sun; they are sources of solar flares, coronal mass ejections and intense UV radiation. Plotting sunspot counts, Schwabe saw that peaks of solar activity were always followed by valleys of relative calm—a clockwork pattern that has held true for more than 200 years: plot.
The current solar minimum is part of that pattern. In fact, it's right on time. "We're due for a bit of quiet—and here it is," says Pesnell.
But is it supposed to be this quiet? In 2008, the sun set the following records:

A 50-year low in solar wind pressure: Measurements by the Ulysses spacecraft reveal a 20% drop in solar wind pressure since the mid-1990s—the lowest point since such measurements began in the 1960s. The solar wind helps keep galactic cosmic rays out of the inner solar system. With the solar wind flagging, more cosmic rays are permitted to enter, resulting in increased health hazards for astronauts. Weaker solar wind also means fewer geomagnetic storms and auroras on Earth.

A 12-year low in solar "irradiance": Careful measurements by several NASA spacecraft show that the sun's brightness has dropped by 0.02% at visible wavelengths and a whopping 6% at extreme UV wavelengths since the solar minimum of 1996. These changes are not enough to reverse the course of global warming, but there are some other, noticeable side-effects: Earth's upper atmosphere is heated less by the sun and it is therefore less "puffed up." Satellites in low Earth orbit experience less atmospheric drag, extending their operational lifetimes. That's the good news. Unfortunately, space junk also remains longer in Earth orbit, increasing hazards to spacecraft and satellites.

A 55-year low in solar radio emissions: After World War II, astronomers began keeping records of the sun's brightness at radio wavelengths. Records of 10.7 cm flux extend back all the way to the early 1950s. Radio telescopes are now recording the dimmest "radio sun" since 1955: plot. Some researchers believe that the lessening of radio emissions is an indication of weakness in the sun's global magnetic field. No one is certain, however, because the source of these long-monitored radio emissions is not fully understood.

All these lows have sparked a debate about whether the ongoing minimum is "weird", "extreme" or just an overdue "market correction" following a string of unusually intense solar maxima.
"Since the Space Age began in the 1950s, solar activity has been generally high," notes Hathaway. "Five of the ten most intense solar cycles on record have occurred in the last 50 years. We're just not used to this kind of deep calm."
Deep calm was fairly common a hundred years ago. The solar minima of 1901 and 1913, for instance, were even longer than the one we're experiencing now. To match those minima in terms of depth and longevity, the current minimum will have to last at least another year.
see captionIn a way, the calm is exciting, says Pesnell. "For the first time in history, we're getting to see what a deep solar minimum is really like." A fleet of spacecraft including the Solar and Heliospheric Observatory (SOHO), the twin STEREO probes, the five THEMIS probes, ACE, Wind, TRACE, AIM, TIMED, Geotail and others are studying the sun and its effects on Earth 24/7 using technology that didn't exist 100 years ago. Their measurements of solar wind, cosmic rays, irradiance and magnetic fields show that solar minimum is much more interesting and profound than anyone expected.
Modern technology cannot, however, predict what comes next. Competing models by dozens of top solar physicists disagree, sometimes sharply, on when this solar minimum will end and how big the next solar maximum will be. Pesnell has surveyed the scientific literature and prepared a "piano plot" showing the range of predictions. The great uncertainty stems from one simple fact: No one fully understands the underlying physics of the sunspot cycle.
Pesnell believes sunspot counts will pick up again soon, "possibly by the end of the year," to be followed by a solar maximum of below-average intensity in 2012 or 2013.
But like other forecasters, he knows he could be wrong. Bull or bear? Stay tuned for updates.

Minimo solare, più senza macchie non si può

Ormai è ufficiale, il disco solare del 2008 è quello con meno macchie di tutti degli ultimi 55 anni, la cosiddetta era spaziale. Ma per chi il sole cerca di studiarlo dentro, spiega la NASA, questo minimo prolungato potrebbe essere una panacea: le macchie rappresentano "rumore" e "perturbazione" per chi deve effettuare misure strumentali e modellamenti.
Intanto però le poche timide macchie che spuntano in questo inizio di ciclo 24 si sciolgono subito riuscendo comunque ad alimentare qualche perturbazione dellla attività geomagnetica.

Spotless Sun: Blankest Year of the Space Age

Sept. 30, 2008: Astronomers who count sunspots have announced that 2008 is now the "blankest year" of the Space Age.

As of Sept. 27, 2008, the sun had been blank, i.e., had no visible sunspots, on 200 days of the year. To find a year with more blank suns, you have to go back to 1954, three years before the launch of Sputnik, when the sun was blank 241 times.
"Sunspot counts are at a 50-year low," says solar physicist David Hathaway of the NASA Marshall Space Flight Center. "We're experiencing a deep minimum of the solar cycle."
The image, taken by the Solar and Heliospheric Observatory (SOHO) on Sept. 27, 2008, shows a solar disk completely unmarked by sunspots. For comparison, a SOHO image taken seven years earlier on Sept. 27, 2001, is peppered with colossal sunspots, all crackling with solar flares: image. The difference is the phase of the 11-year solar cycle. 2001 was a year of solar maximum, with lots of sunspots, solar flares and geomagnetic storms. 2008 is at the cycle's opposite extreme, solar minimum, a quiet time on the sun.
And it is a very quiet time. If solar activity continues as low as it has been, 2008 could rack up a whopping 290 spotless days by the end of December, making it a century-level year in terms of spotlessness.
Hathaway cautions that this development may sound more exciting than it actually is: "While the solar minimum of 2008 is shaping up to be the deepest of the Space Age, it is still unremarkable compared to the long and deep solar minima of the late 19th and early 20th centuries." Those earlier minima routinely racked up 200 to 300 spotless days per year.

Above: A histogram showing the blankest years of the last half-century. The vertical axis is a count of spotless days in each year. The bar for 2008, which was updated on Sept. 27th, is still growing.

Some solar physicists are welcoming the lull.
"This gives us a chance to study the sun without the complications of sunspots," says Dean Pesnell of the Goddard Space Flight Center. "Right now we have the best instrumentation in history looking at the sun. There is a whole fleet of spacecraft devoted to solar physics--SOHO, Hinode, ACE, STEREO and others. We're bound to learn new things during this long solar minimum."
As an example he offers helioseismology: "By monitoring the sun's vibrating surface, helioseismologists can probe the stellar interior in much the same way geologists use earthquakes to probe inside Earth. With sunspots out of the way, we gain a better view of the sun's subsurface winds and inner magnetic dynamo."
"There is also the matter of solar irradiance," adds Pesnell. "Researchers are now seeing the dimmest sun in their records. The change is small, just a fraction of a percent, but significant. Questions about effects on climate are natural if the sun continues to dim."
Pesnell is NASA's project scientist for the Solar Dynamics Observatory (SDO), a new spacecraft equipped to study both solar irradiance and helioseismic waves. Construction of SDO is complete, he says, and it has passed pre-launch vibration and thermal testing. "We are ready to launch! Solar minimum is a great time to go."
Coinciding with the string of blank suns is a 50-year record low in solar wind pressure, a recent discovery of the Ulysses spacecraft. (See the Science@NASA story Solar Wind Loses Pressure.) The pressure drop began years before the current minimum, so it is unclear how the two phenomena are connected, if at all. This is another mystery for SDO and the others.
Who knew the blank sun could be so interesting? More to come...

La NASA alle origini del vento solare

Un volo di 8 minuti per cercare di carpire il segreto del vento solare. Il prossimo mese di aprile la NASA caricherà a bordo di un vettore Black Brant in partenza dalla base del Nuovo Messico uno speciale telescopio. Denominato Solar Ultraviolet Magnetograph Investigation, lo strumento servirà a osservare nell'ultravioletto la cosiddetta regione di transizione nell'atmosfera solare a 5mila metri dalla superficie dell'astro. E' in questa regione, dove il campo magnetico del sole esercita la sua azione di contenimento dei vorticosi gas al suo interno, che si verificano fenomeni come i brillamenti. E dove il vento solare viene inspiegabilmente accelerato fino alla velocità di quasi due milioni di chilometri all'ora. La regione di transizione è il punto di origine dello space weather, della meteorologia spaziale, studiata per cercare di prevedere l'andament o della propagazione radio qui sulla terra. Purtroppo, è anche una regione dove non è facile effettuare misurazioni magnetiche. Sulla superficie del sole le macchie vengono analizzate sfruttando un fenomeno definito per la prima volta dal fisico olandese Pieter Zeeman, che aveva scoperto che immergendo in un campo magnetico una bottiglia riempita di gas, le linee spettrali emesse da questo gas subiscono uno split, una fessura centrale: si spaccano in due longitudinalmente. Più forte è il campo, più ampia e profonda la spaccatura. Grazie allo split di Zeeman gli spettrogrammi delle macchie solari rivelano l'intensità magnetica del fenomeno e possono persino servire per determinane la direzione.
Tutto questo nella regione di transizione non è possibile farlo perché i gas in quella zona non producono linee spettrali nel visibile. Lo fanno nell'ultravioletto, ma qui a terra l'ultravioletto non è ben osservabile. Da cui la necessità di spedire un telescopio UV a una quota sufficientemente elevata: 300 chilometri. Sarà un volo morto corto, ma si spera indicativo. Servirà soprattutto a capire che cosa fare "dopo", quali strumenti utilizzare su quali tipi di sonde.

NASA to Explore "Secret Layer" of the Sun

Sept. 5, 2008: Next April, for a grand total of 8 minutes, NASA astronomers are going to glimpse a secret layer of the sun.

Researchers call it "the transition region." It is a place in the sun's atmosphere, about 5000 km above the stellar surface, where magnetic fields overwhelm the pressure of matter and seize control of the sun's gases. It's where solar flares explode, where coronal mass ejections begin their journey to Earth, where the solar wind is mysteriously accelerated to a million mph. It is, in short, the birthplace of space weather. Researchers hope it is about to yield its secrets.
"Early next year, we're going to launch an experimental telescope that can measure vector magnetic fields in the transition region," explains Jonathan Cirtain of the Marshall Space Flight Center (MSFC). Previous studies have measured these fields above and below the transition region—but never inside it. "We hope to be the first."
The name of the telescope is SUMI, short for Solar Ultraviolet Magnetograph Investigation. It was developed by astronomers and engineers at the MSFC and is currently scheduled for launch from White Sands, New Mexico, in April 2009.
SUMI works by means of "Zeeman splitting." Dutch physicist Pieter Zeeman discovered the effect in the 19th century. When a glass tube filled with incandescent gas is dipped into a magnetic field, spectral lines emitted by the gas get split into two slightly different colors—the stronger the field, the bigger the splitting. The same thing happens on the sun. Here, for instance, are some spectral lines from gaseous iron being split by the magnetic field of a sunspot:


Zeeman splitting of spectral lines from a strongly-magnetized sunspot








By measuring the gap, astronomers estimate the strength of the sunspot's magnetic field. Furthermore, by measuring the polarization of the split line, astronomers can figure out the direction of the magnetic field. Strength + direction = everything you ever wanted to know about a magnetic field!
This trick has been applied to thousands of sunspots on the solar surface, but never to the transition region just a short distance above.
Why not?
"Just bad luck, really," says Cirtain. "Gas in the transition region doesn't produce many strong spectral lines that we can see at visible wavelengths." It does, however, produce lines at UV wavelengths invisible from Earth's surface.
SUMI will blast off inside the nose cone of a Black Brant rocket on a sub-orbital flight that takes it to an altitude of 300 km. "We'll be above more than 99.99% of Earth's atmosphere," says Cirtain. About 68 seconds into the flight, payload doors will open, affording SUMI a crystal-clear view of the UV sun. "From that moment, we've only got 8 minutes to work with. We'll target an active region and start taking data."
SUMI's "vector magnetograph" is tuned to study a pair of spectral lines: one from triply-ionized carbon (CIV) at 155 nanometers and a second from singly-ionized magnesium (MgII) at 280 nanometers. "There's nothing special about those ions," notes Cirtain. "They just happen to produce the best and brightest lines at temperatures and densities typical of the transition region."
Cirtain anticipates how it will feel to have his precious instrument hurtling 300 km above Earth at 5,000 mph: "Eight minutes of terror." He'll start breathing again when the payload doors close and SUMI begins its descent back to Earth. Cirtain ticks off the stages: "Reentry into the atmosphere. Open parachutes. Landing back at White Sands. Recovery."
The short flight probably won't lead to immediate breakthroughs. "But it will demonstrate the SUMI concept and show us if it's going to work." A successful flight would lead to more flights and eventually to a SUMI-style magnetograph permanently installed on a space telescope.
"That's the dream," he says. Transition region, prepare to yield...

Sole senza macchie, possibili effetti climatici?

Sembra che alla fine la NOAA abbia rovinato la festa di chi in questi giorni ha celebrato il trascorso mese di agosto come "primo mese senza macchie solari" in un secolo. Se davvero la superficie del sole non avesse mostrato neppura una piccola macchia, sarebbe stata la prima volta dal 1913. In realtà ieri la NOAA ha modificato la sua statistica relativa all'agosto 2008 attribuendo a una formazione osservata sul sole nei giorni 21 e 22 lo status di "mezza macchia". Insomma, un sole quasi illibato ma non del tutto.
La discussione sul minimo solare sta raggiungendo un massimo. Pochi si occupano della questione pensando alla propagazione dei segnali radio (bassa attività equivale a dire bassa probabilità di propagazione sulle frequenze alte delle onde corte, mentre chi si interessa di onde medie è invece molto contento). Le macchie solari vengono piuttosto considerate come possibile fattore nei modelli di previsione del clima e questo articolo di Michael Asher su Dailitech ne parla diffusamente, citando tra l'altro un libro di un climatologo svedese Henrik Svensmark in cui si ipotizza come l'elevata attività solare faccia da schermo alla radiazione cosmica contrastando così la naturale formazione di nuvole e provocando un innalzamento delle temperature (meno nuvole = più radiazione solare che riscalda il terreno). Il discorso viene approfondito su Watts Up With That, il blog di un meteorologo televisivo in pensione che parla di macchie solari e di indice geomagnetico. Ho trovato anche un interessante spazio di discussione sul ciclo solare 24, che proprio non si decide a decollare, frequentato da molti radioamatori.

Sun Makes History: First Spotless Month in a Century
Michael Asher - September 1, 2008

Drop in solar activity has potential effect for climate on earth.

The sun has reached a milestone not seen for nearly 100 years: an entire month has passed without a single visible sunspot being noted.
The event is significant as many climatologists now believe solar magnetic activity – which determines the number of sunspots -- is an influencing factor for climate on earth.
According to data from Mount Wilson Observatory, UCLA, more than an entire month has passed without a spot. The last time such an event occurred was June of 1913. Sunspot data has been collected since 1749.
When the sun is active, it's not uncommon to see sunspot numbers of 100 or more in a single month. Every 11 years, activity slows, and numbers briefly drop to near-zero. Normally sunspots return very quickly, as a new cycle begins.
But this year -- which corresponds to the start of Solar Cycle 24 -- has been extraordinarily long and quiet, with the first seven months averaging a sunspot number of only 3. August followed with none at all. The astonishing rapid drop of the past year has defied predictions, and caught nearly all astronomers by surprise.
In 2005, a pair of astronomers from the National Solar Observatory (NSO) in Tucson attempted to publish a paper in the journal Science. The pair looked at minute spectroscopic and magnetic changes in the sun. By extrapolating forward, they reached the startling result that, within 10 years, sunspots would vanish entirely. At the time, the sun was very active. Most of their peers laughed at what they considered an unsubstantiated conclusion.
The journal ultimately rejected the paper as being too controversial.
The paper's lead author, William Livingston, tells DailyTech that, while the refusal may have been justified at the time, recent data fits his theory well. He says he will be "secretly pleased" if his predictions come to pass.
But will the rest of us? In the past 1000 years, three previous such events -- the Dalton, Maunder, and Spörer Minimums, have all led to rapid cooling. One was large enough to be called a "mini ice age". For a society dependent on agriculture, cold is more damaging than heat. The growing season shortens, yields drop, and the occurrence of crop-destroying frosts increases.
Meteorologist Anthony Watts, who runs a climate data auditing site, tells DailyTech the sunspot numbers are another indication the "sun's dynamo" is idling. According to Watts, the effect of sunspots on TSI (total solar irradiance) is negligible, but the reduction in the solar magnetosphere affects cloud formation here on Earth, which in turn modulates climate.
This theory was originally proposed by physicist Henrik Svensmark, who has published a number of scientific papers on the subject. Last year Svensmark's "SKY" experiment claimed to have proven that galactic cosmic rays -- which the sun's magnetic field partially shields the Earth from -- increase the formation of molecular clusters that promote cloud growth. Svensmark, who recently published a book on the theory, says the relationship is a larger factor in climate change than greenhouse gases.
Solar physicist Ilya Usoskin of the University of Oulu, Finland, tells DailyTech the correlation between cosmic rays and terrestrial cloud cover is more complex than "more rays equals more clouds". Usoskin, who notes the sun has been more active since 1940 than at any point in the past 11 centuries, says the effects are most important at certain latitudes and altitudes which control climate. He says the relationship needs more study before we can understand it fully.
Other researchers have proposed solar effects on other terrestrial processes besides cloud formation. The sunspot cycle has strong effects on irradiance in certain wavelengths such as the far ultraviolet, which affects ozone production. Natural production of isotopes such as C-14 is also tied to solar activity. The overall effects on climate are still poorly understood.
What is incontrovertible, though, is that ice ages have occurred before. And no scientist, even the most skeptical, is prepared to say it won't happen again.

Article Update, Sep 1 2008. After this story was published, the NOAA reversed their previous decision on a tiny speck seen Aug 21, which gives their version of the August data a half-point. Other observation centers such as Mount Wilson Observatory are still reporting a spotless month. So depending on which center you believe, August was a record for either a full century, or only 50 years.

Aiuto, il sole ha esaurito le macchie? (No)

I DXer dell'FM lamentano una stagione deludente per la propagazione E sporadica, anche se le correlazioni tra macchie solari ed E sporadico sono piuttosto labili: se nello strato F della ionosfera la correlazione tra MUF e flusso solare è forte, nella formazione delle nuvole Es concorrono fenomeni e meccanismi non ancora chiari.
In ogni caso c'è un certo livello di preoccupazione per un minimo solare che sembra prolungarsi oltre il dovuto. Si è rotto qualcosa nel meccanismo delle macchie? David Hathaway, fisico della NASA, è andato a controllare e non ha riscontrato particolari anomalie. E' normale che in periodo di minimo il sole indugi anche molto a lungo nella sua "vacanza". Hathaway è andato a confrontare il numero di "giorni senza macchia" nei cicli solari precedenti e ha scoperto che nel 1933...

What's Wrong with the Sun? (Nothing)

07.11.2008

July 11, 2008: Stop the presses! The sun is behaving normally.

So says NASA solar physicist David Hathaway. "There have been some reports lately that Solar Minimum is lasting longer than it should. That's not true. The ongoing lull in sunspot number is well within historic norms for the solar cycle."
This report, that there's nothing to report, is newsworthy because of a growing buzz in lay and academic circles that something is wrong with the sun. Sun Goes Longer Than Normal Without Producing Sunspots declared one recent press release. A careful look at the data, however, suggests otherwise.
But first, a status report: "The sun is now near the low point of its 11-year activity cycle," says Hathaway. "We call this 'Solar Minimum.' It is the period of quiet that separates one Solar Max from another."
During Solar Max, huge sunspots and intense solar flares are a daily occurance. Auroras appear in Florida. Radiation storms knock out satellites. Radio blackouts frustrate hams. The last such episode took place in the years around 2000-2001.
During Solar Minimum, the opposite occurs. Solar flares are almost non-existant while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now.
Although minima are a normal aspect of the solar cycle, some observers are questioning the length of the ongoing minimum, now slogging through its 3rd year.
"It does seem like it's taking a long time," allows Hathaway, "but I think we're just forgetting how long a solar minimum can last." In the early 20th century there were periods of quiet lasting almost twice as long as the current spell. (See the end notes for an example.) Most researchers weren't even born then.
Hathaway has studied international sunspot counts stretching all the way back to 1749 and he offers these statistics: "The average period of a solar cycle is 131 months with a standard deviation of 14 months. Decaying solar cycle 23 (the one we are experiencing now) has so far lasted 142 months--well within the first standard deviation and thus not at all abnormal. The last available 13-month smoothed sunspot number was 5.70. This is bigger than 12 of the last 23 solar minimum values."
In summary, "the current minimum is not abnormally low or long."
The longest minimum on record, the Maunder Minimum of 1645-1715, lasted an incredible 70 years. Sunspots were rarely observed and the solar cycle seemed to have broken down completely. The period of quiet coincided with the Little Ice Age, a series of extraordinarily bitter winters in Earth's northern hemisphere. Many researchers are convinced that low solar activity, acting in concert with increased volcanism and possible changes in ocean current patterns, played a role in that 17th century cooling.
For reasons no one understands, the sunspot cycle revived itself in the early 18th century and has carried on since with the familiar 11-year period. Because solar physicists do not understand what triggered the Maunder Minimum or exactly how it influenced Earth's climate, they are always on the look-out for signs that it might be happening again.
The quiet of 2008 is not the second coming of the Maunder Minimum, believes Hathaway. "We have already observed a few sunspots from the next solar cycle," he says. (See Solar Cycle 24 Begins.) "This suggests the solar cycle is progressing normally."
What's next? Hathaway anticipates more spotless days1, maybe even hundreds, followed by a return to Solar Max conditions in the years around 2012.

Pochi consensi sul ciclo solare numero 24

Mentre la macchia solare 953 continua il suo percorso apparente (è il sole che sta girando sul proprio asse) verso il centro del disco, portando con sé un potenziale di brillamenti e tempeste geomagnetiche per i prossimi giorni, gli scienziati si sono riuniti a Boulder, in Colorado, per discutere delle previsioni relative al prossimo ciclo solare, il numero 24, che dovrebbe iniziare il prossimo marzo per raggiungere il suo picco verso il 2011 (quando probabilmente non ci saranno più molte stazioni in onde corte locali da ascoltare). C'è chi pensa che sarà molto intenso, ma come sempre le proiezioni sono alquanto variabili.

This week in Boulder, Colorado, a group of leading solar physicists met to compare and discuss their predictions for the next solar maximum. On April 25th they held a press conference and announced ... a split decision. One camp holds that Solar Cycle 24 will be intense and peak in 2011; a second group predicts a much weaker maximum in 2012. As a community, solar physicists are still undecided on the best way to predict solar activity. The plot is a summary of 40 different forecasts, none of which agree in detail. The confusion won't last forever. As Cycle 24 unfolds, the sun itself will tell us which is correct.
Researchers were able to agree on one thing: Solar activity is entering a period of deep minimum. Based on declining sunspot numbers and other factors, the cycle should hit rock bottom in March 2008 plus or minus six months.

Questo è il testo parziale del comunicato stampa rilasciato dopo l'incontro cui si riferiva la notizia apparsa oggi su Spaceweather.com. Un approfondimento della notizia si può leggere su Science Daily di ieri.

NEXT SOLAR STORM CYCLE WILL START LATE

Experts Split Over Intensity

The next 11-year cycle of solar storms will most likely start next March and peak in late 2011 or mid-2012 – up to a year later than expected – according to a forecast issued today by NOAA’s Space Environment Center in coordination with an international panel of solar experts.
Expected to start last fall, the delayed onset of Solar Cycle 24 stymied the panel and left them evenly split on whether a weak or strong period of solar storms lies ahead, but neither group predicts a record-breaker. The Space Environment Center led the prediction panel and issued the forecast at its annual Space Weather Workshop in Boulder. NASA sponsored the panel.
“The Space Environment Center’s space weather alerts, warnings, and forecasts are a critical component of NOAA’s seamless stewardship of the Earth’s total environment, from the Sun to the sea,” said retired Vice Adm. Conrad C. Lautenbacher, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator.
During an active solar period, violent eruptions occur more often on the Sun. Solar flares and vast explosions, known as coronal mass ejections, shoot energetic photons and highly charged matter toward Earth, jolting the planet’s ionosphere and geomagnetic field, potentially affecting power grids, critical military and airline communications, satellites, Global Positioning System signals, and even threatening astronauts with harmful radiation. These same storms illuminate night skies with brilliant sheets of red and green known as auroras, or the northern or southern lights.
Solar cycle intensity is measured in maximum number of sunspots – dark blotches on the Sun that mark areas of heightened magnetic activity. The more sunspots there are, the more likely it is that major solar storms will occur.
In the cycle forecast issued today, half of the panel predicts a moderately strong cycle of 140 sunspots, plus or minus 20, expected to peak in October of 2011. The other half predicts a moderately weak cycle of 90 sunspots, plus or minus 10, peaking in August of 2012. An average solar cycle ranges from 75 to 155 sunspots. The late decline of Cycle 23 has helped shift the panel away from its earlier leaning toward a strong Cycle 24. Now the group is evenly split between strong and weak.
“By giving a long-term outlook, we’re advancing a new field—space climate—that’s still in its infancy,” said retired Air Force Brig. Gen. David L. Johnson, director of NOAA’s National Weather Service. “Issuing a cycle prediction of the onset this far in advance lies on the very edge of what we know about the Sun.”
Scientists have issued cycle predictions only twice before. In 1989, a panel met to predict Cycle 22, which peaked that same year. Scientists met again in September of 1996 to predict Cycle 23—six months after the cycle had begun. Both groups did better at predicting timing than intensity, according to Space Environment Center scientist Douglas Biesecker, who chairs the current panel. He describes the group’s confidence level as “high” for its estimate of a March 2008 onset and “moderate” overall for the two estimates of peak sunspot number and when those peaks would occur.
One disagreement among the current panel members centers on the importance of magnetic fields around the Sun’s poles as the previous cycle decays. End-cycle polar fields are the bedrock of the approach predicting a weak Cycle 24. The strong-cycle forecasters place more importance on other precursors extending over a several-cycle history. Another clue will be whether Cycle 24 sunspots appear by mid 2008. If not, the strong-cycle group might change their forecast.
The first year after solar minimum, marking the end of Cycle 23, will provide the information scientists need to arrive at a consensus. NOAA and the panel decided to issue their best estimate now and update the forecast as the cycle progresses, since Space Environment Center customers have been requesting a forecast for over a year.
“The panelists in each camp have clear views on why they believe in their prediction, why they might be wrong, and what it would take to change their minds,” said Biesecker. “We’re on the verge of understanding and agreeing on which precursors are most important in predicting future solar activity.”